View figure.
This section poses some of the most common questions to consider prior to ordering or changing your system. These topics are illustrated in the scenarios presented later in this chapter.
To use an example, consider the expansion of the existing 3-frame system pictured in Figure 37. This system has frames numbered 1, 2, and 4. Each frame has several unused node slots. Frames 1 and 4 have a switch, but Frame 2 does not. Frame 2 is a non-switched expansion frame whose nodes use the switch in Frame 1.
Figure 37. Sample SP Switch system: 3-frames, 1-switch
View figure.
Before you expand your system, plan ahead for how large you want your system to eventually grow. Planning will encourage you to leave unused frame numbers for future expansion, and will help you avoid having to move nodes between frames. You can make the Sample SP Switch System grow by doing any of the following:
|If you are planning a system of clustered enterprise servers, it can |become a larger scale SP system. You can add an SP Switch2 or SP Switch |in a clustered enterprise server configuration. Your system will then |be subject to all the rules for that switch and these servers will become |SP-attached servers. Consider the following: |
Expanding a system can require that the system be shut down for an extended period of time. When adding a frame or switch to the system, there is often a great deal of cable wiring required. If you know that you want your system to grow in the future by adding nodes, frames, or switches, you might want to consider purchasing some of the hardware in advance. By purchasing in advance, you can set up the hardware and cables with the future in mind to avoid probable cable rewiring, node movement, and reconfiguration complexities at a later date. This can substantially reduce the amount of time your system will be down during future expansion activity.
Notice in the Sample SP Switch System that all 8 of the nodes in Frames 1 and 2 could reside in a single frame, but then many expansion choices would require adding a frame, moving nodes, cabling frames to each other, and so on. Such modifications cannot be done without considerable down time. However, the chosen configuration allows for some expansion without any major difficulties.
|If you are considering adding a switch to a system that does not |have any, keep in mind that the SP Switch2 does not support system |partitioning though it does have advantages. See Choosing a switch for more considerations.
If you are thinking about increasing the number of switches in your system, at least one of the following is pertinent when expanding from:
Cables need to be added, but the first switch could continue running until the new switch is ready for installation tests.
Cables must be rerouted. This scenario can cause a significant amount of system down time. For highest availability, consider installing more frames initially, with empty slots for future node additions.
Addition of a switch-only frame requires recabling, typically taking several days to accomplish. This is a complex scenario that requires detailed planning.
Once configured with a switch-only frame, additional frames can be added without cabling changes to other frames. With careful planning, system outages can be reduced, although installation tests do require checking the entire switch network.
Whenever you modify your system by adding additional hardware, your network topology is affected. This section discusses networking topics you should consider prior to adding any hardware to your system:
Every node in your system has a name assigned to it which is resolved by the name server you are using. The name server translates the symbolic name assigned to a node into an Internet address. As you contemplate adding nodes to your system, plan ahead for the names you will assign to the nodes and how your name server will resolve them.
Nodes have Internet addresses assigned to them, as well as names. While you are planning to add nodes to your system, you need to also plan for the additional Internet addresses that will be assigned to these nodes. In addition, while planning the addresses for these network interfaces, you might reserve additional addresses for expansion the next time your system grows.
If you are using a netmask that limits the number of addresses you can have, you can change your netmask to free up addresses, or you can elect to use a different subnet.
You need to be certain that the control workstation is capable of supporting whatever you plan to add. It must have sufficient processor speed, DASD, and other hardware, such as serial ports and Ethernet adapters. You might need to replace the control workstation. See Chapter 2, Question 10: What do you need for your control workstation?.
|You can consider system partitioning in an SP or clustered |enterprise server system that uses the SP Switch, or in a switchless SP |system. Migration install enhancements do not require the system to be partitioned, but there are many situations when partitions might be advantageous, including the following:
The simplest planning guideline with regard to partitioning is to group nodes together in a common frame(s) if they are to belong to the same partition. Even with the System Partitioning Aid (see Chapter 7, Planning SP system partitions) there are some restrictions on subdividing switches. Bounding system partitions along frame boundaries also makes adding expansion frames easier, and keeps the system more available.
In some configurations, a frame can exist that contains nodes and a switch, but the nodes do not use all of the node switch ports. For example, a frame filled with eight wide nodes only uses eight node switch ports, leaving eight ports free. You can add one or more non-switched expansion frames immediately after such a frame to allow the nodes in the non-switched expansion frames to take advantage of these unused switch ports. In the Sample SP Switch System, Frame 2 is a non-switched expansion frame and frame number 3 has been reserved for the addition of a second non-switched expansion frame to share Frame 1's switch.
Similarly, if a frame having a switch is filled with four high nodes, only 4 node switch ports are occupied, leaving 12 unused. Up to 3 non-switched expansion frames can be inserted to make use of these 12 ports. For example, a single frame might be inserted containing any of 4 wide nodes, 4 high nodes, or some mixture of wide and high node types.
Note that the non-switched expansion frame's number is dependent upon the frame to which it is attached. If the frame containing a switch is number 1, the first associated non-switched expansion frame must be numbered 2, the second 3, and the third 4. Therefore, if you foresee adding non-switched expansion frames to your system in the future, number your frames to allow for the insertion of non-switched expansion frames. Otherwise, the frames which immediately follow must be completely reconfigured.
If your system is organized for partitioning, you might want to leave unused slots for additional nodes, adding an extra frame if necessary; or by leaving gaps in the frame numbers to allow specific frame additions. This is particularly useful if the partition needs a mix of thin, wide, and high nodes.
Again, plan ahead for growth when you assign network addresses. This is easier to manage if you have reserved space for growth in your frame and partition layout.
Generally, you might want to have one boot-install server for every sixteen nodes.